Adenosine (Ado) is an endogenous purine nucleoside released by cells as part of the normal metabolic machinery. Ado has wide variety of biological activities, namely potent antiinflammatory and immunosuppressive properties, protective effects in cardiovascular and cerebrovascular ischemia, anticonvulsant effects and modulation effects of platelet aggregation, lipolysis, glycogenesis, blood flow and neurotransmission. Ado shows the biological activities by binding to its receptors anchored in the cell membrane. Therefore, it is the beneficial treatment for many diseases to perform the pharmacological elevation of extracellular Ado concentrations.
Adenosine deaminase (ADA) catalyzes an essentially irreversible deamination of adenosine or deoxyadenosine to inosine or deoxyinosine, respectively. In the last 10 years, ADA, which was considered to be cytosolic, has been found on the cell surface of many cells. Thus, blocking ADA activity with specific inhibitor is the potent way to elevate Ado concentrations in biological systems and the beneficial treatment for many diseases.
Some compounds have been known to have inhibitory activity of ADA (J. Med. Chem. 27, 274-278, 1984; ibid. 31, 390-393, 1988; ibid. 34, 1187-1192, 1991; ibid. 35, 4180-4184, 1992; ibid. 37, 305-308, 1994; ibid. 37, 3844-3849, 1994; and WO98/02166).
Known imidazole compounds with pharmaceutical activity other than ADA inhibitory activity are described in U.S. Pat. No. 4,451,478 and WO97/26883.
Furthermore, some imidazole derivatives having ADA inhibitory activity have been reported, for example, as described in Drug Development Research 28, 253-258, 1993.